Laser modulation for coagulation

ABSTRACT

An apparatus ( 100 ) has a pump module ( 104 ) providing pump energy, a resonator ( 106 ) and a controller ( 187 ). The resonator ( 106 ) includes a gain medium ( 102 ) receiving the pump energy from the pump module and producing light; reflective surfaces ( 110, 156, 158, 160, 162 ) reflecting light produced by the gain medium back toward the gain medium; and a variable light attenuator ( 152 ) receiving light produced by the gain medium. The controller ( 187 ) controls the amount of light attenuated by the variable light attenuator such that the apparatus emits windows ( 306, 308, 310 ) of pulses of laser light at spaced time intervals, each window containing a plurality of pulses of laser light and each interval ( 326, 327 ) between windows being larger than an interval ( 318 ) between pulses within a window. The emitted windows of pulses ( 320, 322 ) of laser light heat tissue to a temperature that causes coagulation without vaporization.

BACKGROUND

During some medical treatments, laser light is used to ablate tissue byheating it until it vaporizes. During such vaporization, neighboringtissue is typically heated to the point where coagulation occurs, thuspreventing bleeding at the site. However, in some instances, theprocedure does not result in complete coagulation in the neighboringtissue and some bleeding occurs.

In the past, surgeons have attempted to stop any bleeding that occursafter vaporization by applying a lower intensity laser light to thebleeding sites in an effort to induce coagulation without vaporizingadditional tissue.

The discussion above is merely provided for general backgroundinformation and is not intended to be used as an aid in determining thescope of the claimed subject matter.

SUMMARY

An apparatus has a pump module, a resonator and a controller. Theresonator includes a gain medium receiving pump energy from the pumpmodule and producing light; reflective surfaces reflecting lightproduced by the gain medium back toward the gain medium; and a variablelight attenuator receiving light produced by the gain medium. Thecontroller controls the amount of light attenuated by the variable lightattenuator such that the apparatus emits windows of pulses of laserlight at spaced time intervals, each window containing a plurality ofpulses of laser light and each interval between windows being largerthan an interval between pulses within a window. The emitted windows ofpulses of laser light heat tissue to a temperature that causescoagulation without vaporization.

A method receives an input indicating that a medical laser system is tobe placed in a vaporization mode. Based on the input, the medical lasersystem is controlled so that the medical laser system emits a continuousseries of micropulses of laser light. An input is received indicatingthat the medical laser system is to be placed in a coagulation mode.Based on the input, the medical laser system is controlled so that themedical laser system emits a series of macropulses of laser light, eachmacropulse comprising a series of micropulses of laser light and themacropulses in the series separated by a time interval that is longerthan a time interval between micropulses within a macropulse.

A method places a laser system in a coagulation mode such that the lasersystem produces sets of pulses of laser light, wherein pulses within aset are separated by a first time interval and the sets of pulses areseparated from each other by a second time interval. The second timeinterval is larger than the first time interval. The laser light isaimed at tissue to cause coagulation without causing vaporization oftissue.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter. The claimed subject matter is not limited to implementationsthat solve any or all disadvantages noted in the background.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a laser system.

FIG. 2 is an example of a user interface.

FIG. 3 is a graph of laser light intensity over time showing macropulsesfor coagulation.

FIG. 4 is a graph of laser light intensity over time showing acontinuous series of micropulses for tissue vaporization.

FIG. 5 is a graph of the magnitude input to the Q-switch driver overtime.

FIG. 6 is a graph of the on/off input to the Q-switch driver over time.

FIG. 7 is a graph of the magnitude of the Q-switch driver output overtime based on the magnitude input and on/off input of FIGS. 5 and 6.

FIG. 8 is a graph of the laser light intensity over time based on thegraph of the magnitude of the Q-switch driver output of FIG. 7.

FIG. 9 is a flow diagram of a method of using a laser system.

FIG. 10 is a graph of the magnitude input to the Q-switch driver overtime for triangular macropulses.

FIG. 11 is a graph of the on/off input to the Q-switch driver over timefor triangular macropulses.

FIG. 12 is a graph of the magnitude of the Q-switch driver output overtime based on the magnitude input and on/off input of FIGS. 10 and 11.

FIG. 13 is a graph of the laser light intensity over time based on thegraph of the magnitude of the Q-switch driver output of FIG. 12.

DETAILED DESCRIPTION

FIG. 1 is a schematic illustration of a laser system 100 in accordancewith some embodiments. Laser system 100 emits a laser beam 164 using apump module 104, a resonator 106 with a gain medium 102, an opticalcoupler 166, an optical fiber 168, and a delivery tip 170.

In one embodiment, gain medium 102 is a doped crystalline host that isconfigured to absorb pump energy 108 generated by pump module 104, wherepump energy 108 has a wavelength that is within an operating wavelength(i.e., absorption spectra) range of gain medium 102. In one embodiment,gain medium 102 is end-pumped by pump energy 108, which is transmittedthrough a folding mirror 110 that is transmissive at the wavelength ofpump energy 108. Gain medium 102 absorbs pump energy 108 and throughspontaneous emission and stimulated emission outputs light 112.

In some embodiments, gain medium 102 is water cooled (not shown) alongthe sides of the host (not shown). In one embodiment, gain medium 102includes an undoped end cap 114 bonded on a first end 116 of gain medium102, and an undoped end cap 118 bonded on a second end 120 of gainmedium 102. In one embodiment, second end 120 is coated so that it isreflective at the pump energy wavelength, while transmissive at aresonant mode of resonator 106. In this manner, the pump energy that isunabsorbed at second end 120 is redirected back through gain medium 102to be absorbed.

Resonator 106 is configured to generate a harmonic of the light 112output from gain medium 102. In one embodiment, resonator 106 alsoincludes a non-linear crystal (NLC) 150, such as a lithium borate (LBO)crystal or a potassium titanyl phosphate crystal (KTP), for generating asecond harmonic of light 112 emitted by gain medium 102.

In one embodiment, gain medium 102 comprises a yttrium-aluminum-garnetcrystal (YAG) rod with neodymium atoms dispersed in the YAG rod to forma Nd:YAG gain medium 102. The Nd:YAG gain medium 102 converts the pumplight into light 112 having a primary wavelength of 1064 nm. Resonator106 then generates the second harmonic of the 1064 nm light, which has awavelength of 532 nm. One advantage of the 532 nm wavelength is that itis strongly absorbed by hemoglobin in blood and, therefore, is useful inmedical procedures to cut, vaporize and coagulate vascular tissue.

Resonator 106 also includes reflective surfaces in the form ofreflecting mirrors 156, 158 and 162 and folding mirror 110 as well as anoutput coupler 160. The mirrors 110, 156, 158 and 162, and outputcoupler 160 are highly reflective at the primary wavelength (e.g., 1064nm). The output coupler 160 is highly transmissive at the secondharmonic output wavelength (e.g., 532 nm). The primary wavelength laserbeam (e.g., 1064 nm) inside resonator 106 bounces back and forth alongthe path between mirrors 158 and 162, passing through gain medium 102and non-linear crystal 150 to be frequency doubled to the secondharmonic output wavelength (e.g., 532 nm) beam, which is dischargedthrough output coupler 160 as output laser beam 164. The Z-shapedresonant cavity can be configured as discussed in U.S. Pat. No.5,025,446 by Kuizenga.

Resonator 106 includes a Q-switch 152 that operates with gain medium 102and the reflective surfaces of resonator 106 to form pulses of laserlight with high peak power. Q-switch 152 is an externally-controlledvariable light attenuator that can be set to either attenuate light inresonator 106 so that it cannot return to gain medium 102 or allow lightto reflect back to gain medium 102. When light is prevented fromreturning to gain medium 102, the stimulated emission of light withingain medium 102 is prevented and laser light is not produced byresonator 106. While Q-switch 152 is active and attenuating light inresonator 106, gain medium 102 continues to absorb energy from pumpmodule 104 creating a population inversion. When Q-switch 152 isswitched quickly from attenuating light to not attenuating light, alarge stimulated emission occurs in gain medium 102 thereby forming apulse of laser light with a high peak intensity.

Q-switch 152 may be a mechanical device such as a shutter, chopperwheel, or spinning mirror/prism placed inside the cavity. However, inmost embodiments, Q-switch 152 is some form of modulator such as anacousto-optic device or an electro-optic device. In an acousto-opticdevice, an acoustic wave is formed in a scattering medium. The lightbeam enters the medium in a direction forming a Bragg angle to the wavesurface thereby causing the light beam to be diffracted. The acousticwave is formed in the scattering material by applying a driver signal178, typically in the MHz range and produced by a Q-switch driver 180,to a transducer coupled to the scattering material within Q-switch 152.Thus, when driver signal 178 is active, light is diffracted by Q-switch152 and laser system 100 does not produce a laser beam. When driversignal 178 is inactive, light passes through Q-switch 152 without beingdiffracted and laser system 100 produces a laser beam 164. The amount ofscattering provided by Q-switch 152 is controlled in part by themagnitude of driver signal 178 such that the peak intensity of the laserbeam is in part dependent on the difference between the magnitude ofdriver signal 178 during the lowest intensity of the laser beam and themagnitude of driver signal 178 during the highest intensity of the laserbeam. As that difference increases, the peak intensity increases.

An optical coupler 166 receives output laser beam 164 and introduceslaser beam 164 into optical fiber 168. The optic fiber generallycomprises multiple concentric layers that include an outer nylon jacket,a buffer or hard cladding, a cladding and a core. The cladding is bondedto the core and the cladding and core operate as a waveguide that allowselectromagnetic energy, such as laser beam 164, to travel through thecore.

Laser beam 164 is guided along optic fiber 168 to side-firing deliverytip 170, which emits the laser beam at an angle to the axis of opticfiber 168 under some embodiments. During use, the delivery tip 170 ispositioned so that laser beam 164 is incident on tissue to be ablated orcoagulated.

Q-switch driver 180 produces driver signal 178 based on a magnitudeinput 182 and an on/off input 184. Magnitude input 182 is an analoginput that sets the magnitude of driver signal 178, wherein a largermagnitude driver signal produces more diffraction than a lower magnitudedriver signal. On/off input 184 is a digital input that controls whetherdriver signal 178 is on or off. For example, when on/off input 184 has avalue of 0, driver signal 178 is off and no diffraction occurs; whenon/off input 184 has a value of 1, driver signal 178 is on and theamount of diffraction is controlled by the value on magnitude input 182.

In FIG. 1, magnitude input 182 is provided by a digital-to-analogconverter 186, which converts a digital magnitude value stored inmagnitude register 188 into an analog value for magnitude input 182. Thedigital magnitude value is stored in magnitude register 188 by processor190 based on instructions in a control program 192 executed by processor190.

On/off input 184 is generated by a timer 194 based on values stored in amode register 197, a pulse width register 196 and a frequency register195 by processor 190 based on instructions in control program 192. Moderegister 197 is connected to mode inputs 193 of timer 194 and setsvalues that can place the timer into one of three states: a static onstate, a static off state, and an oscillating state. In the static onand static off state, timer 194 fixes on/off input 184 to a respectivevalue of zero or one. In the oscillating state, timer 194 alternateson/off input 184 between zero and one based on values in pulse widthregister 196 connected to duration input 191 of timer 194 and frequencyregister 195 connected to frequency input 189 of timer 194.Specifically, timer 194 sets on/off input 184 to a value of 0 at timepoints that are separated by a time period equal to one over thefrequency in frequency register 195. Timer 194 maintains on/off input184 at a value of one for the period of time represented by the value inpulse width register 196 and then sets on/off input 184 to a value of 0for the remainder of the period set by the frequency in frequencyregister 195. Timer 194 and Q-switch driver 180 together form acontroller 187 for Q-switch 152.

Laser system 100 has two modes of lasing operation: vaporization andcoagulation. When operated in the vaporization mode, laser system 100produces a continuous series of laser pulse that are directed towardtissue to vaporize the tissue. When operated in coagulation mode, lasersystem 100 produces macropulses of laser light that are direct towardtissue to coagulate but not vaporize the tissue. The macropulses areseparated by intervals of no laser light and each macropulse contains aseries of micropulses with the time interval between macropulses beinggreater than the time interval between micropulses within a macropulse.

An operator of laser system 100 can place the laser system in either thevaporization mode or the coagulation mode using a mode selection inputdevice 198 of FIG. 1. When a user manipulates input device 198, a signalis provided to processor 190 that indicates the mode of operationdesired by the user. Based on this signal, instructions in controlprogram 192 are executed to change the values in mode register 197 andunder some embodiments to change values in pulse width register 196,frequency register 195, and magnitude register 188. Under someembodiments, input device 198 is a foot pedal with a separate positionfor vaporization mode and coagulation mode. Control program 192comprises computer-executable instructions that are stored on tangiblemedium such as a solid-state memory device, an optical disc, a magneticdisc or some combination of tangible media.

The operator of laser system 100 can also control the intensity of thelaser light emitted in the vaporization mode and the coagulation modeusing a display 199 and an input device 191. As shown in FIG. 2, a userinterface 200 on display 199 allows an operator to set one power level202 for the laser during vaporization and a second power level 204 forthe laser during coagulation. In the example of FIG. 2, the operator hasset a power level of 120 watts for vaporization and has set a powerlevel of 20 watts for coagulation. Using input device 191, which caninclude a keyboard or a mouse for instance, the operator can selectdifferent values for the power level of each mode of operation. Thispower level is used to adjust the amount of pump energy 108 provided bypump module 104 during each mode of operation.

FIG. 3 provides a graph of laser light intensity over time showingvariations in laser beam intensity when laser system 100 is operated inthe coagulation mode. In FIG. 3, light intensity is shown along verticalaxis 300 and time is shown along horizontal axis 302. Three macropulses(also referred to as windows or sets) 306, 308 and 310 are shown, witheach macropulse containing a series of micropulses such as micropulse312 of macropulse 308 and micropulses 316, 320 and 322 of macropulse306. Each micropulse has a duration such as duration 314 for micropulse316 and the micropulses within a series of micropulses are separatedfrom each other by a time interval such as time interval 318 betweenmicropulses 320 and 322. Each macropulse has a duration such as duration324 for macropulse 308 and the macropulses are separated from each otherby an interval containing no laser light such as interval 326 betweenmacropulses 306 and 308 and interval 327 between macropulses 308 and310.

The interval between macropulses, such as interval 326, has a duration328 that is longer than the duration of the interval betweenmicropulses, such as interval 318. Under one embodiment, the micropulseshave a duration, such as duration 314, of between 0.1 and 10microseconds and the interval between micropulses, such as interval 318,is such that the micropulses occur at a frequency of between 5 and 40kHz within a macropulse. In most cases, the duration of the macropulse,such as duration 324, is between 5 and 50 milliseconds and the durationof the interval between macropulses, such as duration 328, is between 10and 1000 milliseconds. In one particular embodiment, the macropulseseach have a duration of 20 milliseconds and the interval has a durationof 60 milliseconds and the micropulses within a micropulse occur with afrequency of 15 kHz and have a duration of 100 nanoseconds.

The duration of the macropulses and the duration of the intervalsbetween macropulses are such that the emitted macropulses of laser lightheat tissue to a temperature that causes coagulation withoutvaporization.

FIG. 4 provides a graph of laser light intensity over time when lasersystem 100 is in a vaporization mode. In FIG. 4, light intensity isshown along vertical axis 400 and time is shown along horizontal axis402. As shown in FIG. 4, when laser system 100 is in the vaporizationmode, it produces a continuous series or train of micropulses 404. Eachmicropulse has a duration 406 and the micropulses are separated fromeach other by an interval 408. Under one embodiment, the micropulseduration is between 1 and 10 microseconds and the interval betweenmicropulses is such that micropulses occur at a frequency of 15 kHz.

In order to produce the continuous series of micropulses 404 of FIG. 4,control program 192 sets a value in mode register 197 to cause timer 194to enter the oscillation mode where it oscillates on/off input 184between one and zero according to the pulse width in pulse widthregister 196 and the frequency in frequency register 195, where thepulse width in pulse width register 196 indicates the amount of timeon/off input 184 should be at one and the frequency provides the numberof times on/off input 184 should transition from zero to one in asecond.

In the example of FIGS. 3 and 4, the peak intensity 350 of themicropulses in the macropulses of FIG. 3 and the peak intensity 450 ofthe pulses in the continuous series of pulses 404 of FIG. 4 are thesame. In other embodiments, different peak intensities may be used fordifferent modes of operation. In addition, in FIGS. 3 and 4, themicropulses occur with the same frequency in the macropulses of FIG. 3and the continuous series of pulses of FIG. 4. In other embodiments, thetwo modes of operation may use different frequencies of pulses.

FIGS. 5, 6, 7, and 8 provide graphs for the value of magnitude input182, the value of on/off input 184, the magnitude of driver signal 178and the intensity of laser beam 164, respectively, over a same time spanwhile laser system 100 is in a coagulation mode. Time is shown along thehorizontal axis in each of FIGS. 5, 6, 7, and 8 with values that occurat the same time in FIGS. 5, 6, 7 and 8 being aligned vertically acrossthose figures. For example, point 500 of FIG. 5 occurs at the same timeas point 600 of FIG. 6, point 700 of FIG. 7 and point 800 of FIG. 8. InFIG. 5, the magnitude of the analog signal on magnitude input 182 isshown on vertical axis 502. In FIG. 6, the binary value on on/off input184 is shown on vertical axis 602. In FIG. 7, the magnitude of driversignal 178 is shown along vertical axis 702. In FIG. 8, the intensity oflaser beam 164 is shown along vertical axis 802.

In FIG. 8, laser beam 164 contains macropulses 804, 806 and 808separated by intervals 810 and 812. Each macropulse 804, 806, and 808contains a series of micropulses and each interval 810 and 812 iswithout micropulses.

During intervals 810 and 812, on/off input 184 of FIG. 6 is set to oneand magnitude input 182 is at a high operating value designated as OPR.This results in a constant high magnitude for driver signal 178 thatcauses Q-switch 152 to diffract light. As a result, laser beam 164 isnot present during intervals 810 and 812.

With the exception of the first micropulse after a long interval such asintervals 810 and 812, the micropulses in laser beam 164 are triggeredby control program 192 causing timer 184 to oscillate such that on/offinput 184 has a series of pulses, such as pulses 604. During each pulsecycle the series of pulses, on/off input 184 briefly falls to zerothereby causing driver signal 178 to briefly drop to zero. When driversignal 178 drops to zero, the energy in gain medium 102 is released andlaser beam 164 provides a corresponding pulse of light.

At the end of an interval, such as intervals 810 and 812, the magnitudeof magnitude input 182 is reduced by control program 192 in order totrigger the first micropulse of a macropulse of laser beam 164. Thefirst micropulse is triggered by reducing the magnitude input 182instead of setting on/off input 184 to zero, because after the longinterval, a larger amount of energy is stored in gain medium 102 than isstored in gain medium 102 between micropulses. If on/off input 184 weresimply set to zero, all of the stored energy would be released,resulting in the first micropulse having a much greater intensity thanthe remaining micropulses of the macropulse. When the magnitude ofmagnitude input 182 is reduced, there is a corresponding drop in themagnitude of driver signal 178. This reduces the amount of diffractionproduced by Q-switch 152 allowing sufficient amounts of light to returnto gain medium 102 to trigger a pulse of laser light 164. Thus, areduction in magnitude input 182, such as magnitude reduction 504,produces a reduction in driver signal 178, such as reduction 704, whichresults in a laser beam micropulse, such as micropulse 820.

FIG. 9 provides a flow diagram of a method of operating laser system100. In step 900, an operator of laser system 100 places laser deliverytip 170 near a site to be treated. At step 902, the operator uses modeselection input device 198 to send a signal to processor 190 to placelaser system 100 in vaporization mode. At step 904, processor 190receives the signal to place the laser system in vaporization mode andat step 906, control program 192 sets values in mode register 197 tocause timer 194 to provide an oscillating signal to Q-switch driver 180.

At step 908, Q-switch driver 180 produces a driver signal 178 (alsoreferred to as a control signal) for Q-switch 152 that causes Q-switch152 to produce a continuous series of pulses of laser light thatvaporizes tissue.

At step 910, the operator uses mode selection input device 198 to send asignal to place laser system 100 in coagulation mode. The input forplacing laser system 100 in coagulation mode is received by processor190 at step 912. At step 914, control program 192 loops between settinga value in mode register 197 to cause timer 194 to provide anoscillating signal to Q-switch driver 180 and setting a value in moderegister 197 that causes timer 194 to provide a static “on” signal.

At step 916, Q-switch driver 180 produces a driver signal 178 (alsoreferred to as a control signal) for Q-switch 152 that causes Q-switch152 to produce macropulses of micropulses with the macropulses separatedby a longer interval than the pulses within the macropulses.

In the embodiments described above, the macropulse have square shapes.However, in other embodiments other shapes are possible for themacropulses. FIGS. 10, 11, 12 and 13 provide graphs for the value ofmagnitude input 182, the value of on/off input 184, the magnitude ofdriver signal 178 and the intensity of laser beam 164, respectively,over a same time span while laser system 100 is in a coagulation modewith triangular macropulses. Time is shown along the horizontal axis ineach of FIGS. 10, 11, 12, and 13 with values that occur at the same timein FIGS. 10, 11, 12 and 13 being aligned vertically across thosefigures. For example, point 1000 of FIG. 10 occurs at the same time aspoint 1100 of FIG. 11, point 1200 of FIG. 12 and point 1300 of FIG. 13.In FIG. 10, the magnitude of the analog signal on magnitude input 182 isshown on vertical axis 1002. In FIG. 11, the binary value on on/offinput 184 is shown on vertical axis 1102. In FIG. 12, the magnitude ofdriver signal 178 is shown along vertical axis 1202. In FIG. 13, theintensity of laser beam 164 is shown along vertical axis 1302.

In FIG. 13, laser beam 164 contains triangular macropulses 1304, 1306and 1308 separated by intervals 1310 and 1312. Each triangularmacropulse 1304, 1306, and 1308 contains a series of micropulses andeach interval 1310 and 1312 is without micropulses. The magnitude of themicropulses in triangular macropulses 1304, 1306, and 1308 increasesover the time span of the macropulse.

During intervals 1310 and 1312, on/off input 184 of FIG. 11 is set toone and magnitude input 182 is at a high operating value designated asOPR. This results in a constant high magnitude for driver signal 178that causes Q-switch 152 to diffract light. As a result, laser beam 164is not present during intervals 1310 and 1312.

During macropulses 1304, 1306 and 1308, magnitude input 182 oscillatesbetween its high operating level OPR and ever-lower levels untilreaching zero. With each successive lower drop in magnitude input 182,the magnitude of the micropulses in laser beam 164 increases so that theoverall shape of the macropulse is triangular.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

What is claimed is:
 1. An apparatus (100) comprising: a pump module(104) providing pump energy; a resonator (106) comprising: a gain medium(102)receiving the pump energy from the pump module and producing light;at least two at least partially reflective surfaces (110, 156, 158, 160,162) reflecting light produced by the gain medium back toward the gainmedium; a variable light attenuator (152) receiving light produced bythe gain medium; a controller (187) that controls the amount of lightattenuated by the variable light attenuator such that the apparatusemits windows (306, 308, 310) of pulses of laser light at spaced timeintervals, each window containing a plurality of pulses of laser lightand each interval (326, 327) between windows being larger than aninterval (318) between pulses within a window, the duration (324) of thewindows and the duration (328) of the intervals between windows beingsuch that the emitted windows of pulses (320, 322) of laser light heattissue to a temperature that causes coagulation.
 2. The apparatus ofclaim 1 wherein the duration (324) of the windows and the duration (328)of the intervals between windows are such that the emitted windows ofpulses (320, 322) of laser light do not cause vaporization of tissue. 3.The apparatus of claim 2 further comprising a user input device (198)that allows the user to select between a vaporization mode and acoagulation mode, wherein when the user selects the vaporization modethe laser production system produces a continuous train (404) of pulsesof laser light that vaporizes tissue and when the user selects thecoagulation mode, the laser production system produces the windows (306,308, 310) of pulses of laser light.
 4. The apparatus of claim 1 whereinwhen the variable light attenuator (152) attenuates more light, theapparatus produces less laser light.
 5. The apparatus of claim 4 whereinthe controller (187) comprises; a driver (180) producing a driver signal(178), the driver having an input (184) for turning the driver signal onand off, the driver signal such that when the driver signal is on thelight attenuator (152) attenuates more light than when the driver signalis off; a timer (194), coupled to the input (184) of the driver forturning the driver signal (178) on and off and applying a timer signalon the input (184) of the driver for turning the driver signal on andoff, the timer providing a cyclical timer signal in a first mode ofoperation and a static timer signal in a second mode of operation, thetimer having a frequency input (189) that defines the frequency of thecyclical timer signal and a duration input (191) that defines a lengthof time that the timer signal turns the driver signal off during thecyclical timer signal.
 6. The apparatus of claim 5 wherein the statictimer signal turns the driver signal (178) on.
 7. The apparatus of claim6 wherein the driver further comprises a magnitude input (182) thatreceives a magnitude value (188) used to set the magnitude (702) of thedriver signal, wherein a larger magnitude driver signal causes the lightattenuator (152) to attenuate more light than a smaller magnitude driversignal and wherein the apparatus further comprises a processor executingcomputer-executable instructions that cause the processor to decreasethe magnitude value (188) at the end of an interval between windows. 8.A method comprising: receiving (904) an input indicating that a medicallaser system (100) is to be placed in a vaporization mode; based on theinput indicating that the medical laser system is to be placed in thevaporization mode, controlling (908) the medical laser system so thatthe medical laser system emits a continuous series of micropulses (404)of laser light; receiving (912) an input indicating that the medicallaser system is to be placed in a coagulation mode; and based on theinput indicating that the medical laser system is to be placed in acoagulation mode, controlling (914) the medical laser system so that themedical laser system emits a series of macropulses (306, 308, 310) oflaser light, each macropulse comprising a series of micropulses (320,322) of laser light and the macropulses in the series separated by atime interval (328) that is longer than a time interval (318) betweenmicropulses within a macropulse.
 9. The method of claim 8 whereincontrolling the medical laser system so that the medical laser systememits a series of macropulses of laser light comprises controlling aq-switch (152) in the medical laser system.
 10. The method of claim 8wherein each macropulse has a duration (324) and wherein the duration(324) of the macropulses and the time interval (328) between macropulsesare such that the laser light emitted by the medical laser system isinsufficient for performing tissue vaporization.
 11. The method of claim10 wherein the duration of each macropulse is between 5 and 30milliseconds.
 12. The method of claim 11 wherein the time intervalbetween macropulses is 60 milliseconds.
 13. The method of claim 8wherein the series of micropulses within a macropulse is at the samefrequency as the continuous series of micropulses.
 14. A methodcomprising: placing (910, 914) a laser system (100) in a coagulationmode such that the laser system produces sets (306, 308, 310) of pulsesof laser light, wherein pulses within a set are separated by a firsttime interval (318) and the sets of pulses are separated from each otherby a second time interval (328), wherein the second time interval islarger than the first time interval; and aiming (900) the laser light attissue to cause coagulation without causing vaporization of tissue. 15.The method of claim 14 further comprising before placing the lasersystem in the coagulation mode: placing (900, 904) the laser system in avaporization mode such that the laser system produces a continuous (404)series of pulses of laser light; and aiming the laser light at tissue tocause (908) vaporization of tissue.
 16. The method of claim 15 whereinthe pulses in the continuous series of pulses of the vaporization modeoccur at the same frequency as the pulses in the sets of pulses of thecoagulation mode.
 17. The method of claim 16 wherein the pulses in thecontinuous series of pulses of the vaporization mode occur with the samepeak intensity (350, 450) as the pulses in the sets of pulses of thecoagulation mode.
 18. The method of claim 14 further comprising using aninterface (200) to set a first power level (202) for the laser lightemitted in the vaporization mode and a second power level (204) for thelaser light emitted in the coagulation mode.
 19. The method of claim 14wherein the sets of pulses have a duration of between 5 and 30milliseconds and the second time interval is between 60 and 100milliseconds.
 20. The method of claim 19 wherein the pulses within a setof pulses occur with a frequency of 15 kHz.